Large-area molecular electronics incorporating highly ordered self-assembled monolayers (SAMs) provide a promising route to the fabrication of reliable and stable nanodevices, as well as a versatile platform to tailor the electronic transport properties at the molecular level (H. B. Akkerman, B. de Boer, J. Phys. Condens. Mat. 2008, 20, 013001; H. B. Akkerman et al., Nature 2006, 441, 69). For small-area molecular junctions, charge transport through SAMs has been intensively studied using a variety of methods, such as scanning tunneling microscopy (STM) (L. A. Bumm et al., J. Phys. Chem. B 1999, 103, 8122), conducting-probe atomic force microscopy (CP-AFM) (V. B. Engelkes et al., J. Am. Chem. Soc. 2004, 126, 14287), nanopore device (W. Y. Wang et al., Phys. Rev. B 2003, 68, 035416), and cross-wire junction (J. G. Kushmerick et al., Phys. Rev. Lett. 2002, 89, 086802). Different methods for large-area junctions were also applied, for instance, using a conductive polymer or graphene multilayers as an interlayer (A. J. Kronemeijer et al., Appl. Phys. Lett. 2010, 97, 173302; G. Wang et al., Adv. Mater. 2011, 23, 755), Hg-droplet-based electrode (Y. Selzer et al., J. Phys. Chem. B 2002, 106, 10432), and eutectic Ga—In (EGaIn) tip-based electrode (R. C. Chiechi et al., Angew. Chem. Int. Ed. 2008, 47, 142). The mechanism of charge transport through alkanethiol SAMs is off-resonant tunneling with a tunneling decay factor β from 0.51 to 1.16 Å−1 (H. B. Akkerman, B. de Boer, J. Phys. Condens. Mat. 2008, 20, 013001). For π-conjugated molecules shorter than ˜3 nm the transport is still dominated by a tunneling mechanism, while hopping conduction has been observed for the π-conjugated molecules longer than ˜3 nm (S. H. Choi et al., Science 2008, 320, 1482). Understanding of relationships between the molecular structure and the charge transport characteristics is still a big challenge. The influence of molecular conformation on the conductance has been investigated on single molecule junctions. For instance, the biphenyl derivatives with smaller torsion angles between two phenyl rings possess higher conductance than those biphenyl derivatives with larger torsion angles (A. Mishchenko et al., Nano Lett. 2010, 10, 156; L. Venkataraman et al., Nature 2006, 442, 904). Moreover, differences between single-molecule and monolayer junctions have been investigated in terms of local molecular environment of a monolayer junction, such as interfacial charge rearrangement, dipole-dipole interactions, and intermolecular Coulomb interactions (D. A. Egger et al., Adv. Mater. 2012, 24, 4403; G. Heimel et al., Adv. Mater. 2010, 22, 2494; M. Leijnse, Phys. Rev. B 2013, 87, 125417).
Electron irradiation causes decomposition of aliphatic SAMs, but induces lateral cross-linking (coupling of the adjacent phenyl rings) in aromatic SAMs. The cross-linking of SAMs gives rise to a carbon nanomembrane (CNM) (A. Turchanin, A. Golzhäuser, Prog. Surf. Sci. 2012, 87, 108) of molecular thickness that exhibits enhanced mechanical strength and thermal stability (X. Zhang et al., Beilstein J Nanotech. 2011, 2, 826). The terms “carbon nanomembrane” and “cross-linked SAMs” can therefore be used synonymously. Carbon nanomembranes have also been described in EP 1 222 498 B1. The carbon nanomembranes in this patent arise from low molecular aromatics which are cross-linked in the lateral direction.
Due to its remarkable mechanical properties, the CNMs can be released from the initial substrate and transferred onto another solid or porous support and thereby form suspended membranes with macroscopic lateral size (C. T. Nottbohm et al., Ultramicroscopy 2008, 108, 885; A. Turchanin et al., Adv. Mater. 2009, 21, 1233). Eck et al. have shown that the CNMs are stable as freestanding membranes and can be transferred. The CNMs have been released from a substrate by selective cleavage of the anchorgroup-substrate bond or by dissolution of the substrate (Eck et al., Adv. Mater. 2005, 17, 2583).
While a molecular junction of SAMs is considered to be an ensemble of many parallel molecular junctions, the cross-linked SAMs or CNMs provide a unique two-dimensional (2D) system of covalently bonded molecular junctions.
Carbon nanomembranes can be used in layer systems for use as a microelectronic device or a capacitor, in which the carbon nanomembrane is used as the insulating layer. Such a layer system comprising carbon nanomembranes has been described in EP 1 712 298 B1. The organic molecules which are cross-linked in the lateral direction are chemisorbed on the substrate. The compounds forming the cross-linked monolayer comprise an anchor group for chemisorption on the substrate. An electrically conductive, ferromagnetic or semiconductor layer is deposited on top of the monolayer. The layer system of EP 1 712 298 B1 comprises a thin isolating layer. It is not intended, however, to provide particularly thin electrodes. In EP 1 712 298 B1, the top working layer is prepared by adsorbing metal atoms or organic molecules on top of the cross-linked monolayer.
Layer systems of the state of the art usually comprise conventional electrodes which are not very light weight. They are also not very flexible and stable. A further disadvantage of conventional microelectronic devices or capacitors comprising layer systems is that they often comprise harmful or toxic components.
Another layer system is disclosed in Shi et al. (Nano Lett. 2014, 14, 1739). The disclosed nanocapacitor comprises a thin hexagonal boron nitride layer as a dielectric. The preparation of boron nitride is complex and it is difficult to prepare thin homogenous monolayers of boron nitride on large areas. Functionalization of boron nitride is not possible.
An article by Woszczyna et al “All-carbon vertical van der Waals heterostructures: Non-destructive functionalization of graphene for electronic applications” in Advanced Materials, vol 26 (2014), 28, 4831-4837, teaches the manfuacture of a heterostructure comprising an amino-terminatied carbon nanomembrane and a single layer graphene sheet grown on an oxidised silicon wafer. The heterostructures can be used for the fabrication of field-effect devices.
It is an object of the present invention to provide a carbon-based, light-weight multilayer structure comprising ultrathin, flexible and stable layers for use as a capacitor with a high energy density and without harmful or toxic components. It is also an object of the present invention to provide a capacitor comprising at least one multilayer structure, a method of manufacture of a multilayer structure and a microelectronic and an energy storage device comprising the capacitor.